There is an ongoing need in the aerospace industry for new high-temperature elastomers that can exhibit and retain useful mechanical, electrical, and other specific properties under extreme environmental conditions.
Polysiloxanes and their derivatives have attracted interest for use as high-temperature elastomers. The unique combination of high-temperature stability and low-temperature flexibility has prompted syntheses of many examples of these polymers containing a myriad of functional groups. Linear polymers and cross-linked polymers that have repeating units made up of diacetylene groups and siloxane groups are disclosed in, for example, U.S. Pat. No. 5,563,181 to Keller et al., U.S. Pat. No. 5,874,514 to Keller et al., and U.S. Pat. No. RE39332 to Keller et al., incorporated herein by reference. Linear polymers and cross-linked polymers and copolymers made up of silarylene and siloxane units are disclosed in, for example, U.S. Pat. No. 5,578,380 to Babu et al., U.S. SIR No. H1612 to Rhein et al., and U.S. Pat. No. 5,346,980 to Babu et al., incorporated herein by reference.
Incorporation of an aromatic unit into the siloxane backbone of polysiloxane polymers improves both mechanical and thermal properties. However, inclusion of an aromatic group increases the glass-transition temperatures for these polymers and restricts their use at extremely low temperatures.
Accordingly, there is a need for the development of a new type of polysiloxane polymer containing one or more aromatic groups that exhibits thermosetting properties, readily tunable glass transition temperatures (from elastomers to plastics), and high thermal and thermo-oxidative stability.